D850 AF issue

[elsid]

I would, kindly,  ask the members/supporters of this site (owners of a D850) to state whether they have encountered the following problem:
The AF of my D850 goes dead under circumstances that nobody (even the Nikon Distributor in Athens) can explain. The problem has occurred in 3 different instances. 1. When I switch on the camera. 2. When I press the AF-on or shutter release buttons trying to focus. 3. When I am just holding the camera doing nothing. I have used the following lenses 85/1.4G, micro 60/2.8G and 300/4 PF with and w/out the TC 14E III.
After a few seconds the AF system is restored with me doing nothing. The camera does not go off and I can take a photo, which is not focused. 
I took the camera to the distributor/representative, they put it thru a scanning machine and they told me that nothing is wrong with the camera.
I insisted, they gave me another camera with a label on the box "QC Sample" to try and see. The same thing happened with the new sample using the same lenses. I did some searching and I found more than one thread (dpreview) mentioning exactly the same problem.
I asked my dealer and he said that no other customer has reported such a problem. I am still waiting for an answer to the solution from the Nikon representative. Has anybody encountered this problem?

[Ilkka Nissilä]

A few times when I was shooting figure skating with the D850 the day after I got the camera last year it didn’t respond when I pressed AF-ON for a few seconds, then it was working again normally. I was shooting a lot of frames and had snapbridge automatic transfer on. After that day I have not seen this happen. I usually keep airplane mode on (it was suggested by Frank). I don’t know if that had an effect or not. One theory which I had was that I may have accidentally been pressing some other button while trying to focus (as the camera was new I might have supported it from the wrong place momentarily). Anyway it seems to work fine now.

[Erik Lund]

Most likely you are touching another button that prevents AF


In AF-S you should not be able to shoot an image that is out of focus

[elsid]

Ilkka, Erik, I have been using the same lenses with other cameras (D810, D500, Df) without a problem. I am certain that I was not pressing any other button and I was using AF-C (with focus-release). As I mentioned in my post, the problem has, also,  occurred when I switched on the camera and when I was just holding the camera waiting for some wildlife. The person I am in contact with from the Nikon representative says it is a matter of sw. I find this explanation a bit strange. If it were true why there are not many reported instances of the problem? My D850 has been updated with the current microcode.

[Erik Lund]

Your camera could have some mechanical defect like for instance a button that is sometimes 'hanging' this will not show on the electrical test.


It could also be the lens release button on the camera is too sensitive; if you hold the camera and activate focus and at the same time slowly depress the lens release button and see when the AF stops working,,,

[Frank Fremerey]

No occurances with my D850, except for cases in which the lens contacts were not perfectly aligned with the contacts of the camera.

Healing sequence: switch of camera, take off lens, clean contacts, put lens back on make sure it really clicks on ... should work

[elsid]

Erik, Frank,
Thank you for your help. I have used 3 different lenses and the problem is present. The lens contacts are OK and my fingers are not touching the lens release button when I hold the camera ready to shoot. What surprised me is that the "QC sample" camera that Nikon gave me to try out,
presented the same problem. The same lenses have been used extensively on the D500 with no problem. I have asked Nikon to take the camera back and give me another, but I am still waiting for a reply. Erik's "hanging button" approach seems plausible, but which button? 

[chambeshi]

No occurances with my D850, except for cases in which the lens contacts were not perfectly aligned with the contacts of the camera.

Healing sequence: switch of camera, take off lens, clean contacts, put lens back on make sure it really clicks on ... should work

Agree with Erik it sounds like a flaky control button.

I can report the same +ve experience with my D850 since early October. Using a range of AFD, G and E lenses. No "hanging fires" or dead moments with my D850 with either the previous firmware or the recent upgrade. Only exception was with what seemed to be dirty contacts with a 24-120 f4G and 300 f2.8G VRII. Fixed after I cleaned both camera and lens contacts with an earbud. But this has occurred less than 5 times in shooting nearly 12 000 frames

I use AFC almost always with back-button focus and Fn1 set to AFC-Single Point.

[Bernard Delley]

On my D850 I just confirmed: resting a finger "lightly" on the lens release button prevents AF.
I use it with the AFS 60mm f2.8G and thge AF-ON button  for my test.

[Erik Lund]

Thank you for confirming this.

[aerobat]

I haven't got a D850 but it could be that Nikon added a micro switch to the lens release pin to unpower the contacts when the lens is in the middle of the mounting / unmounting procedure.
But due to very little travel it may not work reliably. Or it could also be there's a tolerance issue on the camera side contacts.

[Erik Lund]

The switch has been there for many years, but I don't recall when they introduced it,,,


Edit to add:


The issue; Feature or design mistake, is that it is a very light pressure to activate the switch,,,

[elsid]

As I mentioned in my initial post, the AF goes dead in three instances. 1. When I switch on the camera (has happened once so far),
2. when I try to focus (AF-ON or release button), 3. when the camera is hanging idle (but on) from my shoulder. There is no probability that I am touching (even lightly) the lens release button, because of the way I am holding the camera (my left hand below the lens). Besides, I tried to touch the lens release button out of curiosity and see what happens. I had to apply some pressure, not just touch it, for the AF to go dead.
I am still waiting for an answer from Nikon. The problem is not common. Very few instances have been reported on the internet.
Again, it is a bit perplexing that the QC sample from Nikon presented the same problem.

[Erik Lund]

We all agree your camera is defective.


This is a conversation about not accidentally touching the release button when handling the camera during shooting since it leads to the exact same AF issue.

[elsid]

Thanks to all who have taken the time to comment on the subject.